Problem is to open a pop-up and change page in the calling page. To do that, we used BookmarkablePageLink. This one need to set a PageMap and set the attribute target to the page map of the calling page.
When in the calling page, you can get the pageMap name by doing a : getPage().getPageMap().getName().
the problem is that the default page map have a name set to null by default. this can be resolved (I Think, but not sure) by changing the DEFAULT_NAME in PageMap to something else than null. The other possibility is to add a method in webpage called getwindowname() that would return the window name, which is the default name for the default pageMap.